The present invention relates to the storage, retrieval and editing of frame-based coded audio and/or video data particularly, but not essentially, in conjunction with optical disc storage for the data and the use of MPEG-compliant coding schemes.
In recent times, a need has arisen for both domestic and commercial audio and/or video (herein xe2x80x9cA/Vxe2x80x9d) apparatuses to support a greater amount of user interactivity, and arising from this is a need for seamless joining of A/V segments in which the transition between the end of one segment and the start of the next may be handled smoothly by the decoder. This implies that from the user""s point of view there is no perceptible change in the viewed frame rate and the audio continues uninterrupted. Applications for seamless video are numerous, with particular domestic uses including the editing of home movies and the removal of commercial breaks and other discontinuities in recorded broadcast material. Further examples include video sequence backgrounds for sprites (computer generated images); an example use of this technique would be an animated character running in front of an MPEG coded video sequence. Another is a series of character-user interactions presented as short seamless clips where the outcome of an interaction will determine which clip appears next. A development of this is interactive motion pictures where the user (viewer) can influence the storyline. Branch points along the path a user chooses to take through the interactive movie should appear seamless, otherwise the user will lose the suspension of disbelief normally associated with watching a movie.
A problem with frame-based coding schemes, in particular those such as the MPEG-compliant schemes involving predictive encoding between frames for at least the video content, is that it is not possible to simply jump from the last frame in a first group of pictures (GOP) to the first frame of a new GOP, let alone from one arbitrarily selected frame to another. This is due to temporal dependencies, timing and buffering constraints among others, as will be discussed further hereinafter.
It is therefore an object of the present invention to enable readout of stored audio and/or video clips or frame sequences in a way which allows them to be joined without causing perceptible disturbances.
In accordance with the present invention there is provided a data processing apparatus comprising means operable to read sequences of frame-based data from a storage device and to edit the same, such as to link from a first edit point in a first frame sequence to a second edit point in a second sequence, wherein for each of the stored frame sequences a number of the frames (hereinafter referred to as xe2x80x9cI-framesxe2x80x9d) are intracoded, without reference to any other frame of the sequence, a number (hereinafter referred to as xe2x80x9cP-framesxe2x80x9d) are respectively coded with reference to one further frame of the sequence, and the remainder (hereinafter referred to as xe2x80x9cB-framesxe2x80x9d) are respectively coded with reference to two or more further frames of the sequence; the apparatus including bridge generation means configured to create a bridge frame sequence to link the first and second edit points, by selective incorporation of frames from the stored first and second frame sequences and selective recoding of one or more of the frames within the bridge sequence as determined by the coding type (I, P, or B) of the frames from the first and second sequences indicated by the respective edit points.
Also in accordance with the present invention there is provided a method for editing sequences of frame-based data such as to link from a first edit point in a first frame sequence to a second edit point in a second sequence, wherein for each of the frame sequences a number of the frames (hereinafter xe2x80x9cI-framesxe2x80x9d) are intra-coded, without reference to any other frame of the sequence, a number (hereinafter xe2x80x9cP-framesxe2x80x9d)are respectively coded with reference to one further frame of the sequence, and the remainder (hereinafter xe2x80x9cB-framesxe2x80x9d) are respectively coded with reference to two or more further frames of the sequence; the method including the step of creating a bridge frame sequence to link the first and second edit points, the bridge frame sequence incorporating frames from the first and second frame sequences with selective recoding of frames within the bridge sequence being determined by the coding type of the frames from the first and second sequences indicated by the respective edit points.
By use of the bridge sequence generation, which may be effected by a suitably configured subsection of a signal processing apparatus handling data transfer to and from the storage device, a means is provided to address the problem of making video- and/or audio-frame accurate edits in MPEG-compliant and similar program streams where, because of the temporal dependencies and buffering models used in such coding and multiplexing techniques, simple cut-and-paste edits cannot be made at any frame boundary.
Further features of the present invention are recited in the attached claims, the disclosure of which is incorporated herein by reference, and to which the readers attention is now directed. These and other aspects of the invention are further described in terms of exemplary, but non-limiting, embodiments below.